This invention relates to a method of and a device for testing movable magnetic heads of magnetic recording and and reproducing apparatus for recording and reproducing electric signals in a spiral track to find out if the magnetic heads are able to trace a predetermined spiral magnetic track without deviating therefrom.
In one type of magnetic recording and reproducing apparatus for recording and reproducing electric signals in a spiral track, the magnetic head mounted on the turntable moves in revolving motion on the magnetic surface of a fixed magnetic sheet while tracing a spiral track so as to record or reproduce signals. That is to say, the head is arranged to undergo simultaneous rotary motion and radial motion relative to the turntable axis, thereby tracing a continuous spiral path on the fixed magnetic sheet surface. The head may either record signals on this spiral track, or may reproduce signals previously recorded along the same spiral track on the sheet.
Stated with reference to the reproduction of signals previously recorded (e.g. by another head), maintained accurate register of the head with the recorded spiral track is essential for proper signal reproduction. Deviation of the spiral path of the head from the recorded spiral track on the sheet, whether resulting from misalignment of the center of the spiral or from other causes prevents faithful playback of the recorded signals. Therefore, detection and correction of any such deviation are important to assure satisfactory operation of magnetic recording and reproducing devices of the spiral track type.
Heretofore, detection of head deviation has been performed visually, by positioning on the device (in place of a magnetic recording sheet) a transparent sheet bearing a visible spiral track, and watching the traverse of this track by the head. Deviation or misregister of the head is thus determined by ocular observation of departure of the head from the visible track. Such visual inspection requires very close scrutiny for relatively extended periods of time, and is tiring as well as being subject to human error.